1. Field Of The Invention
This invention relates to a novel process for preparing granular rubber. In particular, it relates to a process for preparing granular polymer rubber which comprises mixing sodium silicate with a chloroprene polymer rubber latex to coat the particles with a silicate or polysilicic acid. Next, an alkaline earth metal salt or an acid is added to form an aqueous dispersion of the chloroprene polymer rubber. The chloroprene polymer rubber then precipitates in the form of granules.
As used throughout the specification, the term "chloroprene polymer rubber" encompasses polychloroprene and copolymers of chloroprene and a comonomer.
2. Description Of The Prior Art
In prior art processes, the chloroprene polymer rubber has been used in the form of chips having a certain size. In molding articles from blocks of rubber, the block is weighed and kneaded with a Bambury mixer or by roller mixing. However, it is difficult to obtain automatic weighing and automatic processing of chips of rubber, and the labor requirements for the processing of the rubber are high. Recently, the blending of rubber with various thermoplastic resin has become increasingly important in expanding the field of use of rubber. It is difficult to blend the rubber and thermoplastic resin in a continuous operation. The problem has been the difficulty in feeding the rubber chips continuously at constant speed to a molding machine such as a uniaxial extruder or a biaxial extruder, and consequently, batch type kneading methods have been employed. This has the disadvantage that a long blending period is required for blending the rubber with a resin which increases the cost. Accordingly, it has been proposed to prepare granular rubber which can be easily weighed and handled without these difficulties and can be fed at constant speed to a molding machine. However, chloroprene polymer rubber has high self-tackiness and it is difficult to obtain granular rubber because of this tackiness of chloroprene polymer rubber particles.
Accordingly, there is a need for a process which can readily prepare non-tacky granular chloroprene polymer rubber.